Cast molded silicone hydrogel contact lenses are produced by polymerizing a polymerizable silicone hydrogel lens forming composition in a contact lens mold assembly. The polymerized silicone hydrogel contact lens product is subsequently removed from the mold assembly and undergoes an extraction procedure to form an extracted polymerized silicone hydrogel lens product that is substantially free of extractable components. The extracted polymerized silicone hydrogel lens product is then hydrated in an aqueous liquid, inspected, packaged, sterilized, and distributed.
During the extraction process, each silicone hydrogel contact lens product is typically individually loaded in a pocket or recess of a tray or lens carrier. The tray may include a plurality of pockets or recesses for holding a plurality of silicone hydrogel contact lens products. While in the tray, the silicone hydrogel lens products are exposed to one or more solutions or compositions that may include any one or a combination of organic solvents and water in order to extract the extractable components from the silicone hydrogel lens products. Concurrently therewith or as a separate step at a different station, the silicone hydrogel lens products are hydrated with water, such as deionized water or an aqueous solution.
The silicone hydrogel lens products undergo swelling and shrinking as a result of exposure to solutions used in the extraction and hydration steps. When placed in contact with an alcohol, a pre-extracted silicone hydrogel lens product will expand to a greater degree compared to when soaking in a solution containing only part alcohol, which expands more than when placed in a solution with only water. During these swelling and shrinking episodes, the silicone hydrogel contact lens products are susceptible to surface distortion that may be caused by, for example, the surface of the silicone hydrogel contact lens products being temporarily pressed against or adhering to a carrier pocket surface or recess surface while undergoing swelling and shrinking.
Based on the above, there is a need for a method that substantially reduces surface distortion of silicone hydrogel contact lens products resulting from extraction procedures, as well as improvements in the manufacture of silicone hydrogel contact lenses, such as improvements in extraction procedures.